This invention relates to the inhibition of intestinal cholesterol absorption in mammals and, more particularly, to inhibiting or decreasing intestinal cholesterol absorption by the oral administration of heparin or heparin subfractions. The invention is based upon our discovery of a novel molecular pathway for the absorption of ingested cholesterol/cholesteryl esters and the identification of specific sites in this pathway for drug intervention to decrease intestinal cholesterol absorption.
Atherosclerosis is the leading killer in the United States, and yet detailed understanding of the absorption of cholesterol, an essential factor in the development of atherosclerosis, has remained rather sketchy, despite the fact that restrictions of dietary intake of cholesterol are the mainstay of therapeutic regimens according to current medical practice. It is known that the principal dietary form of cholesterol is a series of related fatty acid esters of cholesterol and that these must be hydrolyzed before intestinal absorption of cholesterol occurs (Treadwell et al., Handbook of Physiology, Alimentary Canal, Section 6, vol. III, 1968). Pancreatic cholesterol esterase is known to catalyze the hydrolysis of cholesteryl esters but knowledge has remained rudimentary concerning these enzymes due to a lack of a general method for their preparation in homogeneous form, to the frequent use of artificial, colorimetric substrates in lieu of cholesteryl ester in their assay and to the failure to minimize or eliminate artifacts due to the presence of pancreatic proteases in their preparation (Srockerhoff et al., (1974) In: Lipolytic Enzymes, Chapter V, pp. 177-192, Academic Press, New York and Ruddet al., (1984) In: Lipases, pp. 185-204, Elsevier, New York). Accordingly, no unified conceptualization of the role of cholesterol esterase, buttressed by experimental documentation, has emerged. Thus, rat pancreatic cholesterol esterase, the most commonly studied one, is reported as a 67,000 (67K) species that hexamerizes in the presence of taurocholate to form an active enzyme (Calame et al., (1975) Arch. Blochem. Biophys. 168: 57-65). Bovine cholesterol esterase is also 67K, but the porcine and human enzymes are reported as 83K and 100K, respectively (Van den Bosch et al., (1973) Biochem. Biophys. Acta 296: 94-104; Momsen et al. (1977) Biochem. Biophys. Acta 486: 103-113; and Guy et al. (1981) Eur. J. Biochem. 117: 457-460). These differences have not been satisfactorily explained nor the role of taurocholate rigorously examined, but some of these dissimilarities may reflect use of colorimetric substrates for assay instead of cholesterol esters.
Because of these deficiencies, no generally accepted hypothesis has been advanced to explain in molecular details the nature of cholesterol absorption in the intestine, no selective inhibitors have been reported, and the mechanism of re-esterification of cholesterol in the intestinal cell before transport to the liver has not been elucidated.
Despite these shortcomings in prior investigations, one of the primary forms of therapy for patients with elevated cholesterol in the blood has been modulation of intestinal cholesterol absorption, either by serious counseling to eat less cholesterol or through the use of bile salt (derived from cholesterol) binding resins such as cholestyramine which are poorly tolerated (Casdorph, H. R. (1976) In: Lipid Pharmacology, pp. 222-256, Academic Press, New York).
Also, because fatty acids, especially saturated ones, play an essential role in atherogenesis, inhibition of their intestinal absorption should diminish rates of atherogenesis.
There has been a continuing need, therefore, for more fundamental knowledge of the mechanism of cholesterol absorption and improved and effective means for inhibiting intestinal cholesterol and fatty acid absorption in mammals.